Device for electrically reproducing sounds



O. BOTHE DEVICE FOR ELECTRICALLY REPHODUCING SOUNDS Filed March 25, 1922 5 Sheets-Sheet 1 Dec. 29, 1925 1,567,230

0. BOTHE DEVICE FOR ELECTRICALLY REPRODUCING SOUNDS Filed March 23, 1922 3 Sheets-Sheet 2 Dec. 29, 1925- 1,567,230

. 0. BOTHE DEVICE FOR ELEGTRICALLY REPRODUCING SOUNDS Filed March 25, 1922 3 Sheets-Sheet 3 Patented Dec. 29, 1925.

OTTO BOTHE, OF STEGLIIZ, NEAR BERLIN, GERMANY.

* DEVICE FOR ELECTRICALLY REPBODUGING SOUNI DS.

Application filed March 23, 1922. Serial No. 546,106.

To all whom it may concern- Be it known that I, of Germany,

lin, Germany, have invent O'rro Borne, a citizen residing at Steglitz, near Bered certain new and useful Improvements in Devices for Electrically lowing 1s a specificatlon.

Reproducing Sounds, of which the fol- This invention relates to electrical soundreproducing devices by which tones are reproduced Without the slightest change of their natural creasing their'loudness to In the electrical repro Words and musical notes,

timbre while amplifying or inany desired extent. duction of spoken the electric waves produced are extraordinary complicated, because waves of the fundamental tone and the partlal tones are superimposed on one another Hence, if ble a true reproduction or form .a combination Wave. the transmission is to render possiof the speech or music the form of the wave resulting from the superimposed tone Waves must be preserved. In particular it is necessary to faithfully preserve the relative intensities of the various partial tones, because it is on this that the correct reproduction of the sound timbre depends.

To accomplish this the means used-for and reproducing the amplified not be affected by mechanical,

inertia. lar, when using electric currents, it is nee-h cssary to obviate the occurrence translating sound must magnetic or electrical In pali iQus of the disturbing effects of inductance because es pecially in cases in which the tone reproduction covers a large range of sound wave frequenc1es-self-1nduct10n alters the form of the current curve and proper reproduction of t The object of the inven remove all theaforesaid thus destroys the he tones.

tion is to radically drawbacks and to provide means for reproducing tones without any change of timbre (ust-inctness, and at the crease their volume or loudness to such an extent that they can be parts of any large hall.

It is well known that and with perfect same time to inheard well in all spoken words and musical sounds can be reproduced by means at an electric are by superimposing on the arc current the current flu by means of a telephonic like. The electric arc ctuations produced transmitter or the is specially well adapted for the reproduction of tones, be-

cause it is an elastic bo dy of air of very high temperature whose volume fluctuates in accordance with the fluctuations of the current strength duces air sound w A drawback of and therefore directly .pro-

aves.

known electrlc are sound reproducing arrangements is that they are not capable of combining distinctness and .purity of reproduction with a loudness that is sufficient for practical is the reason Why the talking, singing and purposes, and this musical are has hitherto not been used for practical purposes.

In order to cause the arc lamp to satisfactorily reproduce the necessary to make rent fluctuations current as great as or translate them without occasioning sounds it receives'it is the amplitudes of the cursuperimposed on the arc possible and to transfer into the arc lamp circuit any disturbing effects through self-induction. This is a condition which none of th e reviously proposed arrangements has ful lled.

By the present rangement is pro known arrangements, all tones as loudly as does this-entirely without distortion of the original tones.

This is. accomplished current fluctuations,

origlnalft'o'nes an in lamp, to be pro invention a device or arduced which, contrary to not only reproduces necessary, but which (1) by causing the corresponding to the conducted through the duced by electric thermionic valves. Whose grid potential is controlled or varied by a sound transmitter (in the broadest sense of the word) directly affected by the son electric cell or the which the sounds able manner, and

nd waves, or by a photolike affected by a film on are recorded in any suit- (2) by providing means for this purpose and for superimposing the tone current fluctuations on the arc current said throufgh which means the uctuations is translation of the accomplished without interference by self-induction, and hence Without distortion. ations may first The original current fluctube superimp frequency current produced high frequency producer and osed on a high by a separate the high frequency current whose wave form is thus determined by the sent through the a from a source of said fluctuations may be re of an arc lamp supplied continuous current, or the the said high frequency current affected bythe fluctuations due to the original tones may itself be can sed to produce an electric 7 stated above, important to obviate all distortions by inertia due to mass, hysteresis etc.', particularly in producing the voice current, and it is also important to make the fluctuations of the primary or original voice current as great as possible so as to be able to achieve the ultimate result with the smallest possible degree of amplification, or with the smallest possible number of amplifiers or amplifying steps. When it is a question of reproducing recorded sound waves, as waves recorded on a relief-film or phonographic record this can be accomplished by means of a discharge gap with an incandescent cathode influencedby the relief film, or, when it is a question of reproduc ing the actual sounds by transforming them into alternating electric currents that afl'ect the electric are, by means of telephonic condenser transmitters which are'connected in parallel to a non-inductive resistance in the grid circuit of the high frequency producer.

The invention is illustrated by way of ex ample in the drawing in which.

Fig. 1 shows an arrangement \for rep-roducing sounds recorded in relief on a tape film whose wavy surfacevibrates a style,

Fig. 2 shows an arrangement in which sound records on a tone film produce corresponding current "fluctuations which are impressed upon high frequency currents, then amplified together with the high frequency current and finally superimposed by induction on a current flowing through an electric are which reproduces the sounds,

Fig. 3 illustrates another modification in which the high frequency current upon which the tone frequency is impressed directly produces the sound emitting arc in an alternating current lamp.

In the arrangement shown in Fig. 1 the sound waves are recorded in relief" on a film f, each prominence on the film corresponding to a crest of a sound wave and each depression on the film corresponding to a hollow between two sound wave crests. A bichroniated gelatin relief film of this kind may be produced by a swelled-gelatin process, the gelatin being coated for example with a metallic or steel covering by electroplating. A style or knife edge engages with the relief film f, the style or knife edge forming the extremity of the short arm pressed down towards the film by a spring m. The

short arm or feeler is connected with a longer arm n and adapted to swing around a pivot at the point where the short and long arm 1!. meet. The long arm n of the feelercarries a small plate a. at its free end, which is connected to'a battery I) from which it derives a. high electrical potential. The plate a, is the anode of a discharge gap in which an electrical discharge is caused to take place by the corresponding cathode l: (oxide cathode) at the other side of the gap, being brought into incandesceiu-e by the heating battery It. The cathode h, when incandescent, ionizes the discharge gap. The incandescent cathode k is connected to'the other pole of the battery 7) through a high non-inductive resistance w and also through parallel paths extending fron the incandescent cathodes k, W, k of a number of thermionic valves 2, '1 r 'tothe grids g g of these valves. a (L or are the anodes of the thermionic valves 0", 1 'r'" and h is the heating battery for the incandescent cathodes k, 7:, The valves rt, 1, 1" are connected 'in parallel to the electrodes of an arc lamp 0 which receives current from a battery of accumulators 1) through a resistance (1. The regulating coil 8 of the are lamp is a-circuit which is independent of the shunt circuit formed by the thermionic valves. A choking coil t is connected in the arc lamp supply circuit so as to prevent the current fluctuations corresponding to the sound waves and sent through the are from passing into the supply circuit and being thus weakened.- Y

When the sound wave record or tone film travels past the feeler n, motions are imparted'to the latter which cause corresponding alterations anode a and the cathode 10." Changes of resistance of the discharge gap are thus prw duced and result in corresponding fluctuations of potential in the grid circuits of the thermionic valves. 'By this means considerably amplified fluctuations of the current flowing through the thermionic valves connected-in parallel to the are are set up so that corresponding fluctuations of the arc lamp supply current are produced and the arc is caused to emit sound waves. The feeler n can be made so-light that, at. the speeds of osoillation'which occur in translating sounds, no disturbances will arise from its inertia. As'the resistance of the discharge gap is very great and can be made about equal to the resistance of the grid circuit, the fluctuations of potential produced at the grid are rla-tively considerable and a high efficiency is obtained. This arrangement thus represents a low-frequency current-fluctuation amplifier in which the grid potential is controlled without giving rise to distortion and without the aid'of a transformer, and in which the curof the gap between the 4 filament P and valves R and R I'ent fluctuations are very considerably amplified by simple means and then impressed upon the electric arc.

In the arrangement shown in Fig. 2 the current fluctuations corresponding to the tone frequencies are superimposed on a high frequency current. This is done for the purpose of enabling thermionic valves adapted for high potential and corresponding higher efiiciencies to be used without deleterious inductive efl'ects occurring when the necessary conversion or transformation of the voice currents of high potential 'to' the lower voltages suitable for the electric arc is carried out. To accomplish this the periodicity of the high frequency current is not changed, but its amplitudes only are caused to fluctuate in the rhythm of the rates of vibration of the tones to be -re-' produced, and hence variations of phase and distortions of the sounds to be'reproduced are obviated.

A source of light oran incandescent lamp a dens are arranged so that a transparent film travelling at a uniform speed passes through a narrow streak of light. The light, whose intensity is weakened more or less according to the opacity of the arts of thefilm (which comprises cross lnes of various degrees of transparency) through which it passes, 1mpinges, after it is reflected by a mirror M arranged at an angle of upon a photoelectric cell Z .(gas cell) consisting of a cathode K of sodium which is connected to the grid G of a thermionic valve R while the anode A of the photoelectric alkali-metallic cell Z is. connected to the incandescent cathode K of-the valve R a high resistance W being also connected to the cathode K in parallel with the anode A. The current sent from'the battery B through the circuit K, G, K A is thus caused to fluctu: ate in accordance with the sound record on the film and these fluctuations cause corresponding fluctuations of potential at the grid G W is a high non-inductive resistance in a by-path of the circuit leading through the photo-electric cell to the grid of the thermionic valve R A and A are anodes of thermionic Current is supplied to the two, valves R and R by abattery B whose positive pole is connected to the anode A of the valve R In the lead from the battery B to the anode A there is an inductance S and a variable condenser C,

the inductance and the condenser G forming an oscillating circuit coupled in a known manner to the grid G of the valve R by means of a coil S By means of this arrangement undamped oscillations of high frequencies are produced in the high fre quency circuit and the current fluctuations corresponding to the sound waves are superimposed on these oscillations. The super-imposition of the sound wave frequencies takes place in the following manner:

The current fluctuations which are produced by means of the photo-electric cell Z affected by the travelling tone film F give rise to corresponding fluctuations of potential at the grid G of the valve R and these fluctuations in turn produce-fluctuations of the anode current through the two valves It and R which correspond to the tone frequency. This gives rise to corresponding changes of the amplitudes of the high frequency oscillations whose eriodicity, however, remains unchanged. Sorresponding changes of the amplitude of the hi h frequency oscillations are produced hereby, but the rate of vibration of the oscillation remains unaltered.- These high frequency oscillations, 01f which the tone frequencies are superimposed, are now amplified without the occurrence of inertia, in a'known manner and to the extent necessary for obtaining the desired loudness, by means of the high frequency amplifier arrangement hereinafter described.

The undamped oscillations in the thermionic valve R instead of being produced automatlcally, may be set up b an external exciting means consisting o a separate source of high frequency current. The auto-excitation of the thermionic valve by means of a reactive coupling can also be substituted by the dynatron circuit arrangement which is based on the utilization of the so-called declining characteristic.

The amplification of the high frequency carrier current which'carries the tone frequency is accomplished in the following manner: Coupled with the coil S of the oscillation circuit I is a coil S which is included in a circuit that extends through the grid G and the incandescent cathode A heated by the heating battery H and arranged in the thermionoic valve R The valve R is supplied with current by the the grid circuit of another thermionic valve B. This translation is accomplished with the aid of the coil S which forms a secondary coil of a transformer G2 and is included in the rid circuit of the valve R. A potential, which is relatively high so as to correspond with the out ut of the valve R is thus applied to the grid of this valve. Since the tone frequency is impressed on the high frequency oscillations at both sides of the zero line, a kind of vibration is produced low zero neutraliz'e each other at each moment. It is therefore necessary to rectify .the high frequency current and this is done I in the following manner: The translation". of the high fre uency oscillations through' to the valve R and from the transformer tni'svalve to the thermionic valve R is carried out in such a way that at all, times only one half, say the positive half, of the high frequency oscillations produce the flucations of potential at the grid,-.which are necessary for operating the valves, To this end an initial potential is applied to the grid, this initial or preliminary potential being negative or positive according, to the characteristic of the valve and being of such magnitude that thepoint lying midway between the positive and-negative crestssof the high frequency oscillations lies at the lower or upperbend of the curve, which represents the characteristic of'the thermionic valve, that is the curve that gives the values of the current in the anode circuit at different grid %otentials and at a constant anode potential;

this means a recti ing effect is obtained w ich results in ahig frequency pulsating uni-directional current being caused to flow in the anode circuits of the valves, the maximum values of this current corresponding to the impressed tone frequency. This rectifying method will, for convenience of description, be called the anode method of rectifying at the bottom or top bend of the characteristic curve of the valve.

The anode circuit of the thermionic valve R which receives current from the battery B4, contains the primary coil of a high freguency transformer T the secondary coil of which has a comparatively small number of. turns. The high tension of the-high frequency current of the last thermionic valve is thus stepped down to a potential corresponding to that of vtheelectric arc,

'whileits current strength is correspondingly I increased.

Y The problem that now remains to be dealt with is to superimpose on the arc of a continuous current are lamp the high frequency current of constant amplitude reduced in the valve R and which, after t e tone frequency has been impressed upon it in the valve B so as to give rise to changes of its amplitudes corresponding tothe sound waves,

rent; is prevented hing ' from entering the continuous current circuit by means of a chok-, ing coilDF. W is a rheostat. In-the' further modification ofthe invention shown in Fig. 3 the arc'of an alternating current are lamp is directly produced by the'high frequency current upon which the tone frequency is impressed. The particuiar'advantages obtained hereby are as folows:

' As the arc is directly produced by, or supplied with, high frequency current the changes of amplitude of the-high frequency current that correspond to the sound vibrations need only amount to a small percentage, as 10 per cent for example, of the normal amplitude of the high frequency current. Since the ratio between the fluctu ations and the normal amplitudes in the different amplifying steps'of the high frequency themlonic valves remains unaltered, it is not necessary to make this ratio any greater at the first step. Hence the fluctuations of the voice current conducted through the circuit in thefirst stage need only be very small. This facilitates the faithful or distortionless translation of the voice currents and also renders it possible to reproduce feeble sounds, or sounds coming from a considerable distance. Since the carrier current is a high frequency current the amplification is attained in the high frequency thermionic valve arrangement without distortion, there being no mass, inductance or hysteresis that-can exert a distorting effect. Any desired degree of-amplification can be obtained in the high frequency amplifier or thermionicvalve. The alternating current are lamp permits of a perfectly continuous and uniform regulation of the gap between its electrodes. By

feeding the arc'with high frequency alternating current the advantage of an ascendcharacteristic of the arc is obtained, that is to say the resistance of the latter, instead of representing a negative value as in ordinary arcs, becomes positive, and is therefore adapted in an increased degree for the faithful reproduction of tones, of all kinds. The acoustic effect of the high frequency alternating current is considerably greater than that of a low frequency undulating unidirectional current for the following reasons The fluctuationsof amplitude of the hi h frequency current that (correspond to t e sound waves are impressed on both sides (positive and negative) of the current curve. The fluctuations of current are therefore twice as great as in the case of a continuous current on which a voice current is superimposed. If electrodes or carbons placed atan angle to each other are usedwhich presents no difficultyin alternating current lamps in which the carbons are both magnetic field the reproduced tone, continuous current from accumulators is consumed at equal rates-the powerful gives rise to very strong pulsations of the arc, and this helps in the production of the air waves that produce the sound. Another point to be noticed is that in a continuous current lamp the so-called commutator noises of the continuous current dynamo are diflicult to eliminate from while the supply of generally not feasible for economical reasons.

In Fig. 3 an alternating current arc lamp arrangement is shown in which 1 is a thermionic valve with an anode 2 and an. incandescent cathode, 3fthat is heated by current supplied from a heating battery, 4 through a resistance 5 of iron. The high frequency current is produced in a known manner by means of an oscillation circuit comprising an adjustable condenser 6 and an inductance 7, and connected to the grid 8 of the valve 1 by a reactive coupling which c mprises a potentiometer arrangement 46.v T

e super-imposition of the tone frequency on the high frequency current, that is to say, the alteration of the amplitudes of the high frequency current in accordance with the ordinates'of the sound wave curve, is accomplished by including a high non-inductive resistance 9 and one or more condensers 10 of comparatively small capacity in theone .wire of the reactive coupling circuit. In

each condenser one condenser-plate is constructed in the form of a diaphragm adapted to approach and recede from its associated plate in "accordance with the sound vibrations. Each condenser thus constitutes a transmitter which is capable of faithfully reproducing the sound waves it receives, backs of a contact or carbon microphone. The high frequency current produced in the high frequency circuit, and the tone frequencies impressed.;;upon it, are translated y induction from the coil 7 to the coil 11 and thus conducted to the grid 12 of a thermionicvalve 13, The amplified high frequency currentis then translated b a coil 14 in the circuit of the anode 13 into the coil 15 which impresses corresponding fluctuations of potential on the grids 16 and 17 of two thermionic valves 18 and 19 connectedin parallel. The anodes of the valves 18 and 19 are connected to an oscillatory circuit comprising an adjustable condenser 20 and an inductance 21, and, in order to obtain a high efficiency, this oscillatory circuit is tuned to the primary oscillatory circuit 6, 7. The high frequency current in the coil 21 induces a corresponding high frequency current in the coil 22, from which the induced current flows through the two electrodes or carbons 23, 24 of an alternating current are lamp. In order to facilitate the tuning of the two oscillatory circults 6, 7

as it'is not subject to the drawand 20, 21 the couplings of all of the coils used for translating the high frequency current oscillations are loose. The are lamp is regulated in a known mannerby a regulating coil 26 in the main circuit and by a regulating resistance or rheostat 27. The electric are 28, on receiving the high frequency current oscillations on which the tone frequencies are impressed, reproduces all the sound vibrations taken in at the re ceiving end'by the diaphragms of the condenser microphone 10. The sound vibrations reproduced by the are are considerablv amplified and quite undistorted.

The entire high-frequency amplifier arrangements 1, 2, 21 maybe supplied with current by a single alternating current machine 29 which produces currents of fairly high frequencies. This current is sent through an autotransformer 30 from which two circuits are branched off in accordance with the potentiometer principle, the one circuit comprising the wires 31, 32 and the other the wires 31, 33.

The circuit 31, 32 contains the transformer coils 34 and 35. The coil 34 induces a current in the secondary coil 35 for heating the incandescent cathode 36 of a Wehnelt rectifier 37 and the coil 35 induces current in a secondary coil-38 which heats the incandescent cathodes 39 and 40 of the two thermionic valves 18 and 19.

The circuit 31, 33 contains the primary coil 41 of a high frequency transformer which receives alternating current of a medium fre uency. This current induces a correspon ing current in the coil 42 which /is conducted to the two anodes 43 and 44 of the rectifier 37. The coil 42 is tapped at the middle. The current stepped up to a high tension in the transformer 41, 42, and conducted through the rectifier 37, flows in the form of a continuous current from the cathode 36 through a wire 45, high resistance 46 and a wire 47 to the middle of the coil 42. Inserted in the wires and 47 are choking coils 48;and 49. Large condensers and 51 are connected across the wires 45 and 47 at both sides of the choking coils 48 and 49. The choking coils 48, 49 and the condensers 50 and 51 form a smoothening arrangement by which any remaining fluctuations of voltage are eliminated and the current made perfectly continuous.

The thermionic valves 1, 13, 18 and 19 are lit) supplied with current from the resistance I 46 on the potentiometer principle through wires 52 and 53, 54 and 55, 56 respective y.

The arrangement to which the invention relates is primarily. intended for reproducing vocal and musical notes in cooperation with films in moving pictures theatres, the sound records being made to travel synchronously with the cinematographic picture film. The invention 1s, however,

novel arrangement is used, the electric arc must be entirely or partly screened off, and this must be done without interfering with the ventilation of the arc lamp. An artifical.

ventilation of the lamp is'pre'ferred, because this enhances the acoustic effect. The devices used t'or screening off the light will preferably be such that the sound waves reach the auditorium by indirect reflection. An arrangement of this kind consisting of an upper conical opaque hood 57 and of a bottom conical opaque cup or basin 58 is shown in F ig.- 3, and a similar device'is also illustrated in Figs. 1 and 2.

I claim be made audible to a large meaaso 1. Injan arrangement for electrically reproduclngsounds, a thermlomc valve, means for covertmg sound waves into corresponding electric fluctuations and for impressing these fluctuations on the grid of the thermionic valve, and an electric arc affected by the anode circuit of the thermionic valve, said arc being connected inparallel to the said anode circuit.

2. In an arrangement for electrically reproducing sounds, a thermionic valve, means for convertin sound waves into corresponding electric uctuations and for imparting these fluctuations to the grid of thethermionic valve, an electric are affected by the anode circuit of the thermionic valve, and two hollow conical screens for screening 0 the light of the arc and reflecting the sound waves-emitted by it in the direction of the .axes of the conical screens.

It testimony whereof I have signed this 7.

specification.

o'r'ro BOTHE. 

